Tx Rx fault finding HELP

Replace the battery in the transmitter.

my

I went and bought a copy of the transistor substitution guides. Sometimes paper is better.....

Mike

: Question 1. How do I determine which cct is at fault ?

REPLACE THE TX REPLACE THE RX

then you will know if the problem is tx or rx related

no spare? then move the rx away from noise sources - ie the computer

first thing I did

gordon

open

voltages

at $43 for a one time use maybe

gordon

no replacements. and I have the Rx off the computer and on a power supply and the CRO shows a nice clean code at the output of the Rx but only at short range (2 to 3 ft) I'm sorry I don't understand what noise might have to do with it, I thought my problem was decreasing sensitivity, i.e. transistors reaching end of life, hence my request for a cross-reference URL. I'd be happy to change all the transistors in both the TX and Rx and get this thing back on the road but I'd really like to have a fault finding procedure for now and the future and a cross-reference of parts.

Gordon

PS: my wife says "another day without HER beeper is divorce material"

ft)

thought

Gordon, unless I've missed something here changing the components is unlikely to help. These components are more likely to fail outright rather than decrease in performance IMHO. I'm unfamiliar with the devices but your twiddling of the tx cap suggests some drifing in frequency in the rx or tx. Is the system radio, ultrasonic or whatever ? If one of the latter two, voltage or contamination of the sensors would be my first port of call. If its radio, then alignment would be the go.

Cheers Jim

shows

Thanks Jim, it's radio and the transistor in the Tx has an ft of 1GHz so I imagine the operating freq is around 300-500MHz or so. It has a coder chip feeding the osc/output transistor and the appropriate coil, caps and resistors. The Rx is similar but has more transistors and an opamp for gain to the decoder chip. Really simple I guess but with only an old CRO and a DMM and no knowledge I'm stuck with tweaking so goodness knows where the alignment is now if both the Tx and Rx have wandered off freq. If you or anyone has an idea how I can get this back on track I'd be most thankful.

Gordon

"Gordon W"

Very simple command transmitters are not generally crystal locked but simply adjusted with a ferrite slug in the tank circuit coil. If it were my problem, I would try using my radio scanner ( AR 1000 XLT), set it to 303.9 MHz and "wide FM" and place it a few metres away - then tune the Tx coil for maximum audio level on the scanner. Next switch the scanner to AM and check the signal that way too. If all goes OK , the Rx is then tuned to give best range.

Frequencies in the range from 273 MHz to 328 MHz might also be tried if

............. Phil

of

get

finding

rather

suggests

ultrasonic

be

chip

gain

Gordon, no idea sorry. I use a comms test set .

simply

Thanks Phil, I'm trying to do that but with the Rx as I haven't got a scanner. For a long time now I've been able to tune the Tx to get back the range but it didn't work this time. Therefore I thought some component must have been moving outside of its specs and should be replaced. I haven't touched the Rx yet so maybe that's where I should head next ie use the Tx as the standard.

Anyway, thank you and all the other people for your help.

Gordon